It is known that a latent electrostatic image can be developed with toner particles dispersed in an insulating nonpolar liquid. Such dispersed materials are known as liquid toners or liquid developers. A latent electrostatic image may be produced by providing a photoconductive layer with a uniform electrostatic charge and subsequently discharging the electrostatic charge by exposing it to a modulated beam of radiant energy. Other methods are known for forming latent electrostatic images. Useful liquid developers comprise a thermoplastic resin, dispersant nonpolar liquid, and charge director. Generally a suitable colorant is present such as a pigment or dye. The colored toner particles are dispersed in the nonpolar liquid which generally has a high-volume resistivity in excess of 10.sup.9 ohm centimeters, a low dielectric constant below 3.0 and a high vapor pressure. The toner particles are less than 10 .mu.m average by area size. After the latent electrostatic image has been formed, the image is developed by the colored toner particles dispersed in said dispersant nonpolar liquid and the image may be used directly or subsequently be transferred to a carrier sheet.
A problem with liquid developers of the past is that they have a grainy appearance, i.e., have nonuniform resolution. Graininess causes unclear images, and reduces the number of gray levels that can be discerned in the images obtained. Another problem is incomplete toning and "toner robbing" where dark-toned image areas deplete toner from light-toned image areas. These phenomena are caused by low toner mobility, i.e., the toner does not travel to the oppositively charged film fast enough to tone to completion.
It has been found that the above disadvantages can be overcome and improved liquid electrostatic developers prepared containing a dispersant nonpolar liquid, charge director and thermoplastic resin particles of an admixture of a multiblock copolymer and a thermoplastic resin.